# What would happen if you turned the Hubble Space Telescope towards Earth? **URL:** \ **Category:** Factual Questions\ **Created:** [February 24, 2014, 7:59am UTC](https://boards.straightdope.com/t/what-would-happen-if-you-turned-the-hubble-space-telescope-towards-earth/682076 "2014-02-24T07:59:29Z")\ **Posts on this page:** 14\ **Page:** 1
**Author:** ![Mr.Kobayashi](https://avatars.discourse-cdn.com/v4/letter/m/4af34b/32.png) [@Mr.Kobayashi](https://boards.straightdope.com/u/Mr.Kobayashi)\ **Post date:** [February 24, 2014, 7:59am UTC](https://boards.straightdope.com/t/what-would-happen-if-you-turned-the-hubble-space-telescope-towards-earth/682076/1 "2014-02-24T07:59:29Z")
I’ve got a feeling that the neighbours cat is crapping in my yard and I want to catch it in the act in the most ostentatious way possible. Say I got control of the Hubble Space Telescope, currently in low Earth orbit and spotting distant galaxies. Could I turn it (or any other space-based telescope) towards Earth? Would the image I got prove the cat did the dirty deed or would the images be worthless to anyone? ---
**Author:** ![Hail\_Ants](https://avatars.discourse-cdn.com/v4/letter/h/dc4da7/32.png) [@Hail\_Ants](https://boards.straightdope.com/u/Hail_Ants)\ **Post date:** [February 24, 2014, 8:18am UTC](https://boards.straightdope.com/t/what-would-happen-if-you-turned-the-hubble-space-telescope-towards-earth/682076/2 "2014-02-24T08:18:17Z")
I’m sure the details are more complex, but basically yes. American KH spy satellites are very similar to the HST in general design… ---
**Author:** ![MrDibble](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mrdibble/32/114_2.png) [@MrDibble](https://boards.straightdope.com/u/MrDibble)\ **Post date:** [February 24, 2014, 8:33am UTC](https://boards.straightdope.com/t/what-would-happen-if-you-turned-the-hubble-space-telescope-towards-earth/682076/3 "2014-02-24T08:33:47Z")
> [@Mr.Kobayashi](#): > > Would the image I got prove the cat did the dirty deed or would the images be worthless to anyone? It’d be worthless, according to former Doper [BadAstronomer](http://www.badastronomy.com/mad/2000/hubbleearth.html). It’d be, at best, a cat-coloured blurred streak, if that. ---
**Author:** ![MrDibble](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mrdibble/32/114_2.png) [@MrDibble](https://boards.straightdope.com/u/MrDibble)\ **Post date:** [February 24, 2014, 8:38am UTC](https://boards.straightdope.com/t/what-would-happen-if-you-turned-the-hubble-space-telescope-towards-earth/682076/4 "2014-02-24T08:38:42Z")
> [@Hail\_Ants](#): > > I’m sure the details are more complex, but basically yes. American KH spy satellites are very similar to the HST in general design… Very different orbits, though. ---
**Author:** ![Isilder](https://avatars.discourse-cdn.com/v4/letter/i/cc9497/32.png) [@Isilder](https://boards.straightdope.com/u/Isilder)\ **Post date:** [February 24, 2014, 9:36am UTC](https://boards.straightdope.com/t/what-would-happen-if-you-turned-the-hubble-space-telescope-towards-earth/682076/5 "2014-02-24T09:36:42Z")
The atmosphere pretty much limits effective pixel size to be at least 10cm. Having more pixels (reducing them to 5cm or 2 cm or 1cm) isn’t giving any better detail, its just blur. So no satellite is going to identify the cat, all it will show a cat as a few pixels… a 15 pixel cat isn’t high enough res… Spy satellites can prove a school bus drove across your back yard… not a cat ---
**Author:** ![chorpler](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chorpler/32/2888_2.png) [@chorpler](https://boards.straightdope.com/u/chorpler)\ **Post date:** [February 24, 2014, 11:44am UTC](https://boards.straightdope.com/t/what-would-happen-if-you-turned-the-hubble-space-telescope-towards-earth/682076/6 "2014-02-24T11:44:21Z")
XKCD had a “what if” answering this exact question. [Hubble](https://what-if.xkcd.com/32/) ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [February 24, 2014, 3:47pm UTC](https://boards.straightdope.com/t/what-would-happen-if-you-turned-the-hubble-space-telescope-towards-earth/682076/7 "2014-02-24T15:47:37Z")
The Earth is also much brighter than the things the Hubble was designed to look at. If you’re not very careful about limiting your exposure times, you could burn out some of the instruments. It looked at the Moon once, but even that was pushing it, and the Earth is considerably brighter than the Moon. ---
**Author:** ![Mr.Kobayashi](https://avatars.discourse-cdn.com/v4/letter/m/4af34b/32.png) [@Mr.Kobayashi](https://boards.straightdope.com/u/Mr.Kobayashi)\ **Post date:** [February 24, 2014, 4:14pm UTC](https://boards.straightdope.com/t/what-would-happen-if-you-turned-the-hubble-space-telescope-towards-earth/682076/8 "2014-02-24T16:14:00Z")
Fascinating, thanks for the very thorough answers. Would I have better luck with its future successor, the James Webb Space Telescope? It seems planned to have a far larger orbit than Hubble. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [February 24, 2014, 4:21pm UTC](https://boards.straightdope.com/t/what-would-happen-if-you-turned-the-hubble-space-telescope-towards-earth/682076/9 "2014-02-24T16:21:33Z")
You’d get less motion blur, but the brightness would be even more overwhelming, and the resolution would be far less, both due to the instrument and its distance. ---
**Author:** ![Grey](https://avatars.discourse-cdn.com/v4/letter/g/b782af/32.png) [@Grey](https://boards.straightdope.com/u/Grey)\ **Post date:** [February 24, 2014, 4:32pm UTC](https://boards.straightdope.com/t/what-would-happen-if-you-turned-the-hubble-space-telescope-towards-earth/682076/10 "2014-02-24T16:32:57Z")
> [@Mr.Kobayashi](#): > > Fascinating, thanks for the very thorough answers. Would I have better luck with its future successor, the James Webb Space Telescope? It seems planned to have a far larger orbit than Hubble. Hubble is designed for optical wavelengths while the JWST is focused on infra-red. ---
**Author:** ![Artemis\_Tardis](https://avatars.discourse-cdn.com/v4/letter/a/4bbf92/32.png) [@Artemis\_Tardis](https://boards.straightdope.com/u/Artemis_Tardis)\ **Post date:** [February 24, 2014, 4:48pm UTC](https://boards.straightdope.com/t/what-would-happen-if-you-turned-the-hubble-space-telescope-towards-earth/682076/11 "2014-02-24T16:48:31Z")
Also, I think that focus could be a potential problem… Question: what is the resolution of the sensor on Hubble? ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [February 24, 2014, 4:57pm UTC](https://boards.straightdope.com/t/what-would-happen-if-you-turned-the-hubble-space-telescope-towards-earth/682076/12 "2014-02-24T16:57:11Z")
Focus won’t matter. The Hubble has a focal length of a few meters, and is orbiting at a height of hundreds of kilometers. That’s close enough to “infinity” for practical matters. ---
**Author:** ![EdwardLost](https://avatars.discourse-cdn.com/v4/letter/e/bbe5ce/32.png) [@EdwardLost](https://boards.straightdope.com/u/EdwardLost)\ **Post date:** [February 24, 2014, 8:25pm UTC](https://boards.straightdope.com/t/what-would-happen-if-you-turned-the-hubble-space-telescope-towards-earth/682076/13 "2014-02-24T20:25:25Z")
> [@Chronos](#): > > and the Earth is considerably brighter than the Moon. Why? Because of the clouds? The oceans? Or is moon rock just dark? ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [February 24, 2014, 8:48pm UTC](https://boards.straightdope.com/t/what-would-happen-if-you-turned-the-hubble-space-telescope-towards-earth/682076/14 "2014-02-24T20:48:17Z")
All of the above.